The use of polyoxyalkylene amines as epoxy curatives is well known and is described, for example in U.S. Pat. No. 4,485,229. In U.S. Pat. No. 4,051,195 and copending application Ser. No. 801,984, there are also described formulations of epoxy and polyoxyalkylene amine and which utilize Michael addition of the amine to the acrylic component to provide crosslinking between the epoxy and acrylic components.
It is also known to use polyimides or various functionalized imide compounds, e.g., aminoimide compounds, in epoxy formulations, see e.g., U.S. Pat. Nos. 3,985,928, 3,763,087, and 4,092,442.
In U.S. Pat. No. 3,988,299 there are described anaerobic acrylic adhesives which display improved high temperature strength as a result of inclusion of a maleimide or nadimide compound.
In U.S. Pat. No. 4,490,515 there are described cyanoacrylate adhesives with maleimide or nadimide additives having improved strength at elevated temperatures.
While the use of maleimide or nadimide functional compounds as additives to improve hot strength various curable adhesive or related systems has been previously described, applicants are unaware of any prior art suggesting that such additives can result in improved adhesion or thermal cycle resistance (i.e. resistance to loss of adhesion as a result of repeated large temperature changes.)
A major feature of the new engineering plastics that have been used for electronic applications is their thermal and dimensional stability. Thermal coefficients of expansion (TCE) of &lt;30.times.10.sup.-5 inch/inch deg C. are common. Usually the electrical/electronic component is of composite structure containing plastic, ceramic and metal components. This situation is typified by potentiometers. Adhesive/Potting Compounds are used to encapsulate and protect electrical components from adverse environmental effects such as solvents or moisture. The adhesive component must retain its adhesion throughout the range of service conditions. One of the most severe tests the adhesive must withstand is delamination induced because of the difference TCE's of the construction materials of electrical/electronic component.
Adhesive systems most commonly used to pot/encapsulate and bond electrical/electronic components are one and two-part epoxy resins. The resins are filled to a high level with mineral fillers, e.g., aluminum trihydrate to reduce shrinkage and TCE. However, these resins do suffer from significant process disadvantages such as slow cure. Moreover, their initial adhesion and thermal cycling properties are still not always entirely satisfactory.
Traditional UV curable acrylic compositions are unsuitable due to high shrinkage on polymerization 8-15% and high TCE (of the order of 90.times.10.sup.-5 inch/inch deg C.).
U.S. patent applications Ser. No. 801,984, filed Nov. 26, 1985, Ser. No. 882,670, filed July 7, 1986, now abandoned and Ser. No. 926,312, filed Oct. 31, 1986 now abandoned describe compositions which exhibit advantages over both epoxies and UV curable acrylics. However, even these new materials can sometimes prove unsuitable for bonding electrical/electronic components of composite structure where extreme thermal cycling and thermal shock is application requirement, i.e., -50.degree. C. to 165.degree. C.